Multistage manufacturing systems (MMS) are commonplace, diverse in variety and are employed in various aspects of many manufacturing industries. Complex mechanical assemblies, such as automatic transmissions, and vehicle assembly plant processes, such as body assembly operations, are examples of MMS related specifically to assembly systems. However, MMS are also widely employed in complex fabrication systems, e.g. semi-conductor fabrication, and complex machining systems, e.g. internal combustion engine block and head machining. Some hybrid MMS include aspects from multiple types of manufacturing systems including assembly, fabrication and machining.
A common characteristic of MMS is a multiplicity of well defined processing operations and stations. MMS also typically involve multiple fixture exchanges and process datum changes. This is particularly evident in the complex machining and assembly of engine blocks and heads or of transmission cases, for example.
Variations throughout MMS affect the quality of the final manufactured product. Each of the multiplicity of operations and stations and associated transfers of workpieces therebetween are potential sources for introducing variation into the final product. Trial and error approaches are commonly employed in improving quality of parts produced by machining MMS. However, such techniques tend to be lengthy and not generally well structured and understood with respect to specific manufacturing variables.
Practices are known for simulating component part tolerance stack-up in assembly processes and for providing conformance-type analysis of such simulations. Final product conformance to print may thereby be statistically predicted and component tolerances adjusted—relaxed or tightened—to effect quality and cost improvements to the final product.
Complex machining processes, however, include a variety of inputs and sensitivities not generally shared by assembly systems or other types of manufacturing systems. For example, machining variations can be affected by variations in raw castings, variations in accuracy and repeatability of machine motion, geometric variations of the workpiece and fixture, station transfers and fixture changes, elastic deformation of the workpiece and fixtures due to clamping forces, and machining variations due to cutting forces.